As shown in FIG. 19, in a solid polymer fuel cell, a membrane electrode assembly (MEA) comprising an electrolyte membrane 92 formed from a solid polymer film sandwiched between two electrodes, namely a fuel electrode 96 and an air electrode 94, is itself sandwiched between two separators 90 to generate a cell that functions as the smallest unit, and a plurality of these unit cells are then usually stacked to form a fuel cell stack (FC stack), enabling a high voltage to be obtained.
The mechanism for electric power generation by a solid polymer fuel cell generally involves the supply of a fuel gas such as a hydrogen-containing gas to the fuel electrode (the anode side electrode) 96, and supply of an oxidizing gas such as a gas comprising mainly oxygen (O2) or air to the air electrode (the cathode side electrode) 94. The hydrogen-containing gas is supplied to the fuel electrode 96 through fuel gas passages, and the action of the electrode catalyst causes the hydrogen to dissociate into electrons and hydrogen ions (H+). The electrons flow through an external circuit from the fuel electrode 96 to the air electrode 94, thereby generating an electrical current. Meanwhile, the hydrogen ions (H+) pass through the electrolyte membrane 92 to the air electrode 94, and bond with oxygen and the electrons that have passed through the external circuit, thereby generating reaction water (H2O). The heat that is generated at the same time as the bonding reaction between hydrogen (H2), oxygen (O2) and the electrons is recovered using cooling water.
In recent years, fuel cell structural members in which the membrane electrode assembly and gas diffusion layers are molded as a single integrated unit have been proposed to enable unit cells to be constructed with a minimal number of components (for example, see Patent Document 1). As illustrated in FIG. 20, this type of fuel cell structural member comprises an MEA composed of an electrolyte membrane 1 and gas diffusion layers 2 and 3 integrally molded to the two sides of the electrolyte membrane 1 with catalyst-supporting layers 2a and 3a that constitute the electrodes disposed therebetween, and further comprises impregnated band portions 2b and 3b formed from a liquid rubber or synthetic resin which extend inwards for a predetermined width from the peripheral edges of the gas diffusion layers 2 and 3, and a gasket 4 formed from an elastic material is integrally molded so as to totally cover the outer surfaces of the impregnated band portions 2b and 3b. 
Further, as illustrated in FIG. 21, a membrane electrode assembly disclosed in Patent Document 2 comprises reinforcing layers 5 provided on both surfaces of an electrolyte membrane 1, wherein catalyst layers 2a and 3a are each laminated to a portion of the respective reinforcing layer 5, and gas diffusion layers 2 and 3 are then laminated thereon. On the other hand, in a manifold opening 11 of the membrane electrode assembly, the reinforcing layers 5 are provided on both surfaces of the electrolyte membrane 1, an adhesive layer 8, a spacer layer 6 and an impregnated portion 7 are laminated to each reinforcing layer 5, and a sealing portion 9 is formed on the surface of each impregnated portion 7 both inside and outside the manifold opening 11 in the in-plane direction. Accordingly, as illustrated in FIG. 21, by forming the adhesive layers 8 and the spacer layers 6 around the outer periphery of the membrane electrode assembly, extending the outer peripheral portions of the gas diffusion layers 2 and 3 of the anode and cathode respectively through to the manifold region, and then forming the impregnated portions 7 by impregnating these outer peripheral portions of the gas diffusion layers with a sealing material, a membrane electrode assembly can be provided in which the gas diffusion layers can be prevented from biting into the assembly under the compressive stress generated during molding, enabling damage to the electrolyte membrane to be suppressed.    Patent Document 1: JP 2006-236957 A    Patent Document 2: JP 2007-42348 A